1. Field of the Invention
The present invention relates to a multiple light source type light pipe which can form a planar light source unit excellent in light utilizing efficiency and excellent in brightness and its uniformity, and a reflection type or transmission type liquid-crystal display device bright and easy to view, and which can provide an emission light color conversion system.
The present application is based on Japanese Patent Application No. Hei. 11-331205, which is incorporated herein by reference.
2. Description of the Related Art
A heretofore known light pipe is a side-lighting type light pipe made of a plate-like member having rough surfaces or white dots provided in one of its upper and lower surfaces for scattering light incident on its side surfaces to thereby output the light to the other of its upper and lower surfaces. Such a side-lighting type light pipe is used as follows. That is, a light source is disposed on the side surfaces of the light pipe to thereby form a planar light source unit. The planar light source unit is combined with a liquid-crystal cell to thereby form a reflection type or transmission type liquid-crystal display device.
There was, however, a problem that the light pipe was inferior in brightness and its uniformity and inferior in display quality. Although there was a proposal to dispose light sources on a plurality of side surfaces in order to improve brightness, it was difficult to improve the variation of the brightness. In a system in which a diffusing layer or a prism sheet was disposed in order to control an optical path, the number of parts was increased so that production efficiency was lowered. Incidentally, liquid-crystal display devices are classified into a back-lighting group and a front-lighting group by the position of arrangement of the planar light source unit relative to a liquid-crystal cell. In the aforementioned scattering system, there was a problem that it was difficult to use the scattering system as a front-lighting system because the scattering system disturbed a display image. Such a front-lighting system has been in demand for improvement so that the front-lighting system can exchange light emission colors in the same manner as the back-lighting system with the advance of popularization of display devices to portable telephone sets, etc.
An object of the present invention is to develop a light pipe which can form a planar light source unit excellent in light utilizing efficiency and excellent in brightness and its uniformity, and which can form a reflection type or transmission type liquid-crystal display device bright and easy to view, and which can be applied to a front-lighting system so that light emission colors can be exchanged.
According to an aspect of the present invention, there is provided a light pipe comprising a plate-like member at least having an upper surface, a lower surface, and incidence side surfaces constituted by opposite two side surfaces between the upper surface and the lower surface. The plate-like member further has light output means in one of the upper and lower surfaces so that light incident on each of the incidence side surfaces is made exit from the other of the upper and lower surfaces through the light output means. The light output means is constituted by a repetitive structure of irregularities having ridgelines along the incidence side surfaces, each of the irregularities having a pair of transmission light reflection surfaces which face the incidence side surfaces respectively, the transmission light reflection surfaces are inclined in directions opposite to each other, and having a pair of gentle slopes which are disposed between the pair of transmission light reflection surfaces, each of the gentle slopes is inclined in a directions opposite to the inclination direction of adjacent one of the transmission light reflection surfaces.
According to another aspect of the present invention, there is provided a planar light source unit comprising the above-mentioned light pipe, and light sources disposed on the incidence side surfaces, respectively, of the light pipe. According to a further aspect of the present invention, there is provided a reflection type liquid-crystal display device comprising the above-mentioned planar light source unit using a light pipe made of a plate-like member having a light output means in an upper surface of the plate-like member as described above, and comprising a reflection layer-including liquid-crystal cell disposed on a lower surface of the light pipe of the planar light source unit. According to another aspect of the present invention, there is provided a transmission type liquid-crystal display device comprising the above-mentioned planar light source unit using a light pipe made of a plate-like member having a light output means in an upper surface or a lower surface of the plate-like member as described above, a transmission type liquid-crystal cell disposed on the upper surface of the light pipe of the light source unit, and a light reflection means disposed on the lower surface of the light pipe.
According to the present invention, light from light sources are made to be incident on two side surfaces of a light pipe so that the incident light exits from one and the same surface through alight output means constituted by a repetitive structure of irregularities. Hence, light from the light sources can be converted efficiently to form a planar light source. Hence, a planar light source unit excellent in brightness and its uniformity can be obtained. When the planar light source unit is used as a back-lighting or front-lighting system, a reflection type or transmission type liquid-crystal display device bright and easy to view can be formed. Further, a liquid-crystal display device using a front-lighting or background system in which light emission colors can be changed in combination of heterochromous emission light sources can be also formed.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.